Add the ability to suspend the runtime at startup to connect to EventPipe

[shirhatti]

It isn't currently possible to profile startup code using dotnet-trace as there's currently no way to suspend the runtime till a client has connected to EventPipe.

This is a regression in functionality compared to the controller file mechanism in 2.x that allowed profiling startup code.

[josalem]

The beginnings of this feature were built for doing stress testing of the connection mechanism: dotnet/coreclr#24936. I could see this functionality being expanded on. Something like dotnet trace collect <options> -- <dotnet dll> <args> could be invoked and dotnet-trace sets the appropriate environment variable in the sub-process's environment, so that it waits until the tool has attached.

[shirhatti]

@josalem Do we still need this issue? Or good to close because of reversed pipe?

[josalem]

This is what I'm currently working on. We have a reversed pipe, but the runtime doesn't stop on start yet.

[sywhang]

Closing this issue as the runtime side work has shipped with 5.0 rc and the tools work has been completed with #1635.